Fix several issues with .xinitrc

.xinitrc

@@ -1,14 +1,33 @@
 [ -f ~/.xprofile ] && . ~/.xprofile
 [ -f ~/.setpath.sh ] && . ~/.setpath.sh
 
-DEFAULT_SESSION=qtile
+AUTHORISED_WM="qtile i3"
+AVAILABLE_WM=""
+REQUESTED_WM="$1"
 
-case "$1" in
-    awesome)
-	exec awesome
-	;;
-    qtile)
-	exec qtile 2>/tmp/qtile.err.log
-	;;
-    *) exec $DEFAULT_SESSION ;;
-esac
+for wm in $AUTHORISED_WM; do
+    if hash "$wm" 2>/dev/null; then
+        if [ "$AVAILABLE_WM" ]; then
+            AVAILABLE_WM="$AVAILABLE_WM $wm"
+        else
+            AVAILABLE_WM="$wm"
+        fi
+    fi
+done
+if [ ! "$AVAILABLE_WM" ]; then
+    >&2 echo "Error: No window manager found. Please install one of the following:"
+    >&2 echo "$AUTHORISED_WM"
+    exit 1
+fi
+
+WM=$(echo "$AVAILABLE_WM" | tr ' ' '\n' | head -n1)
+if [ "$REQUESTED_WM" ]; then
+    found=$(echo "$AVAILABLE_WM" | tr ' ' '\n' | grep -w "$REQUESTED_WM")
+    if [ "$found" ]; then
+        WM="$found"
+    else
+        >&2 echo "Warning: $REQUESTED_WM not found, starting the default window manager."
+    fi
+fi
+
+exec "$WM" 2>/tmp/xinit.err.log